1. Field of the Invention
The invention relates to a process for developing irradiated radiation-sensitive recording materials using an aqueous-alkali developer containing specific compounds.
2. Description of Related Art
An aqueous-alkali developer for radiation-sensitive recording materials, in particular those from which offset printing plates are produced, must satisfy a number of requirements It should be productive. This means that the development efficiency should diminish as little as possible even after extended use and thus increased content of stripped-off layer constituents. The so-called "tone limit", at which the developer is consumed and the layer is stripped off only incompletely in the non-image areas, should be as high as possible. It should develop the recording materials as quickly and completely as possible. This is particularly important in the machine production of printing plates on processing lines. Short cycle times mean that a development duration of significantly less than 30 seconds may be necessary.
The areas of the recording material which later take up the printing ink (the image areas) should be subject to as little attack by the developer as possible. Only then is it ensured that no image damage occurs even after repeated development, as is possible, for example, in photocomposing
During development, no foam or solid precipitates should form. The latter could contaminate the development equipment and thus make increased service costs necessary or they could even be deposited on the developed recording material
In addition, the development should allow hard gradation. Only then are the pixels transferred precisely from the film master to the plate, with even small dots being reproduced precisely
For ecological and economic reasons, it is advantageous if the developer can be supplied in the form of a liquid or solid concentrate which is first diluted with water by the consumer. The water hardness varies from region to region, but this should not affect the properties of the ready-to-use developer. There is consequently a requirement for low sensitivity to water hardness.
Finally, the recording material support must not be attacked by the developer. In the case of the aluminum support material frequently used for printing plates, the aluminum oxide layer, in particular, should remain intact during development.
The developers known hitherto do -not simultaneously satisfy all said requirements. In particular, developers produced from concentrates exhibited unsatisfactory properties
Developers which are extremely sensitive to water hardness are those which contain amines, hydroxides, phosphates, silicates, borates, and carbonates as alkaline constituents It has therefore been attempted to avoid this disadvantage by adding ethylenediamine-tetraacetic acid, diethylenetriaminepentaacetic acid or nitrilotriacetic acid or salts of these compounds. The developers modified in this way again attack the support to a greater extent. Neither was the addition of di-, tri- or polyphosphates suitable for reducing the dependence on the water hardness, since these compounds were hydrolysed in the alkaline developers
DE-A 33 15 395 describes a concentrate containing an alkali metal silicate and a chelating agent. Dilution with tap water gives a developer for recording materials containing an orthoquinone diazide in the photosensitive layer. The chelating agent prevents the calcium and magnesium ions in the tap water from reacting with the alkali metal silicate to form insoluble material Preferred chelating agents are organic phosphonic acids and phosphonotricarboxylic acids, such as aminotris-methylenephosphonic acid or ethylenediaminotetra-methylenephosphonic acid. However, these chelating agents are not biodegradable.